1. Field of the Invention
This invention relates to nondestructive testing and, more particularly, to nondestructive detection of surface flaws in objects. A flaw may be a chip, fingerprint, scratch, pit, or any other deviation from a smooth surface. This invention specifically relates to measurement of surface flaws in spherical objects such as ball bearings.
2. The Prior Art
Computational procedures have been developed to find the mechanical resonances of objects other than a sphere but which also have some symmetries. This work is described in "On the modes of free vibrations on inhomogeneous and anisotropic elastic objects" by Visscher et al., J. Acoust Soc. Am., 90 (4) p. 2154, 1991. Examples are, objects, such as a cylinder, rectangular parallel piped, cone, ellipsoid, or pyramids with regular polygon bases.
Testing of objects by use of sound (including ultrasound) and vibrations is well known. The prior art is extensive and encompasses many types of non-destructive testing. Resonant sound and ultrasound has also been used for testing purposes as described in U.S. Pat. Nos. 5,062,296, 4,976,148, and 5,355,731 which are incorporated herein by reference, except for their incorporation by reference of other information.
Also incorporated herein by reference is U.S. patent application Ser. No. 08/075,210 entitled Ultrasonic Differential Measurement filed Jun. 10, 1993, now U.S. Pat. No. 5,408,880. Applicant does not incorporate into this application any material which was incorporated into these prior patent applications by reference.
In U.S. Pat. No. 5,355,731 entitled, "Sphericity Determination Using Resonant Ultrasound Spectroscopy," there is described a method of analysis which is specific to sphericity determination. One mode of employment of RUS relates the resonant ultrasound spectrum of a component to the dimensions and material properties of the components.